1. Field of the Invention
The invention relates to a semiconductor wafer processing systems, and, in particular, to a backside gas delivery system for a semiconductor wafer processing system.
2. Description of the Background Art
Electrostatic chucks (ESC) are used in many single-wafer processing systems for retaining wafers during processing. In order to improve heat conduction between the wafer and the chuck, a backside gas supplied between the wafer and the support surface of the chuck is often used as a heat transfer medium. The design of a backside gas delivery system may have significant impact on the performance of the wafer processing system, especially in cases where stringent pressure control is required.
An ion implanter, such as the one described in commonly assigned U.S. Pat. No. 6,179,921, issued Jan. 30, 2001, entitled xe2x80x9cBackside Gas Delivery System For A Semiconductor Wafer Processing Systemxe2x80x9d, and incorporated herein by reference, teaches an ion implanter that generates a beam of a selected specie of ions (e.g., dopant ions) and directs the beam towards a target wafer positioned on an electrostatic chuck of a wafer support assembly. Implantation is typically used for producing regions in the semiconductor wafer having an altered conductive state. In particular, the implanter implants ions of the dopant under the surface of the wafer. The ion beam generator is stationary, while the wafer support assembly is movably positioned facing the ion beam generator. Additionally, the chuck of the wafer support assembly is rotatable. During the ion implanting process the chuck rotates to permit the ion beam to strike predefined portions of the wafer. Such rotational movement of the chuck is limited by the internal and external chuck components attached thereto.
Furthermore, the Ruffell patent application teaches a backside gas delivery system having the gas shutoff valve disposed in the spindle. In particular, a backside gas supplied to the support assembly is provided by a flexible tubing from a gas source. The flexible tubing has a length that permits the chuck to rotate or move in any plane. However, the integrity of the flexible tubing becomes degraded during the course of repeated wafer processing and chuck rotation. For instance, as the chuck rotates, the flexible tubing wraps or coils around the support assembly, which subjects the flexible tubing structural stresses and fatigue. Eventually, gas leaks may occur, which reduce the backside gas delivered to the backside of the wafer. A reduction in backside gas will correspondingly reduce the amount of heat that may be transferred from the wafer, which may ultimately damage the wafer during processing. Furthermore, such gas leaks may enter the vacuum chamber and subsequently contaminate the wafer during processing.
Therefore, a need exists for a reliable backside gas delivery system that provides a heat transfer gas to the backside of the wafer, while permitting full rotational capabilities of the chuck during wafer processing.